Study on the soft mode around the phase transition tenperature of ferroelectric crystals through low-frequency dielectric spectrum measurements.

通过低频介电谱测量研究铁电晶体相变温度附近的软模。

• 批准号: 06640458
• 负责人: DEGUCHI Kiyoshi
• 金额: $ 1.28万
• 依托单位: Shizuoka Institute of Science and Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 1995
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06640458/
• 关键词: ferroelectrics; phase tansition; soft mode; critical relaxational mode; 誘電分散

The measurement system of low-frequency dielectric spectrum has been developed. This measurement system is able to speedly provide reliable measurement data in the frequency region of 45 MHz to 15 GHz, and in the temperature region of 80 K to 450 K.The dielectric spectra of ferroelectric crystals, LHP,LHA,TSCC and D-LTT have been investigated by using the developed measurement system. The results are summarized as follows ;1.Apparent dielectric critical slowing-down are found around the phase transition temperatures of LHP and LHA.The results indicate that the mechanism of the ferroelectric phase transition is of an order-disorder.2.TSCC is known to be the first example which shows both the critical softening of phonon mode and the critical slowing-down of the ralaxational mode. The present study clarifies that the critical relaxational mode reported previously is not the relaxational mode but the over-damped soft mode.3.Critical relaxational mode is not observed in deuterated LTT (D-LTT), as in not-deuteraterd LTT.The nature of the phase transition is not affected by deuteration. However, It is found that the displacive ferroelectric LTT shows unusual deuteration effect of phase transition ; the transition temperature is lowered with increasing the ratio of deuteron. The ferroelectric phase transition disappears in the crystal with the deuteration ratio more than 95%.

研制了低频介电谱测量系统。该测量系统能够在45 MHz ~ 15 GHz的频率范围和80 K ~ 450 K的温度范围内快速提供可靠的测量数据。利用该测量系统对铁电晶体、LHP、LHA、TSCC和D-LTT的介电谱进行了研究。结果表明：（1）在LHP和LHA的相变温度附近存在明显的介电临界慢化现象，表明其铁电相变机制是有序-无序的;（2）TSCC是第一个同时表现出声子模临界软化和弛豫模临界慢化的例子。本研究澄清了先前报道的临界弛豫模不是弛豫模而是过阻尼软模。3.在氘代LTT（D-LTT）中没有观察到与非氘代LTT一样的临界弛豫模，相变的性质不受氘代的影响。然而，发现位移型铁电体LTT表现出异常的相变氘化效应，相变温度随氘化率的增加而降低。当氘化率大于95%时，晶体中的铁电相变消失。

项目成果

K.Deguchi: "Comparative Studies on the Dielectric Properties of Hydrogen-Borded Ferroelectric PbHAsO_4 and PbHPO_4" to be published.

K.Deguchi：“氢键铁电PbHAsO_4和PbHPO_4介电性能的比较研究”即将出版。

Y.Iwata, S.Mitani, I.Shibuya, K.Deguchi and E.Nakamura: "Neutron Diffraction Study on CDP-DCDP Mixed Crystals" Ferroelectrics. Vol.170. 1 (1995)

Y.Iwata、S.Mitani、I.Shibuya、K.Deguchi 和 E.Nakamura：“CDP-DCDP 混合晶体的中子衍射研究”铁电体。

Y.Kobayashi: "X-ray Diffraction and Dielectric Constant Measurement of KH_2PO_4 under High Pressure" Proc.Joint XV AIRAPT & XXXIII EHPRG Int.Conf.Warsaw. 242-244 (1995)

Y.Kobayashi：“高压下 KH_2PO_4 的 X 射线衍射和介电常数测量”Proc.Joint XV AIRAPT

Y.Iwata: "A Neutron Diffraction Study on the Deuteration Effect in CsH_2PO_4" J.Phys.Soc.Jpm.63. 4044-4050 (1994)

Y.Iwata：“CsH_2PO_4 氘化效应的中子衍射研究”J.Phys.Soc.Jpm.63。

K.Deguchi: "Comparative Studies on the Dielectric Properties of Hydrogen-Bonded Ferroelectric PbHAsO_4 and PbHPO_4" (to be published).

K.Deguchi：“氢键铁电PbHAsO_4和PbHPO_4介电性能的比较研究”（待出版）。